1. Field of the Invention
The present invention relates to a method of washing and cleaning a plurality of membrane filtration units aligned in series, each of said units being part of a circuit provided with a recirculation pump, whereby the respective unit of each of the circuits can be fed with liquid to be purified and impure liquid be discharged, which either serves as a supply for a consecutive circuit or which is discharged by subsequently introducing a washing liquid whether or not containing washings bodies, through the respective membrane filtration units, aligned in series.
2. Description of the Prior Art
In the prior art a method for washing and cleaning a plurality of membrane filtration units aligned in series has been used. During the use of membrane filtration units, impurities will accumulate upon the membrane surfaces, which surfaces contacts liquids to be purified; the presence of said impurities may give rise to a decrease in the action of said membranes. In order to remove the impurities a constant washing and cleaning of the membranes in membrane filtration units is required.
Often said washing and cleaning is effected with a desinfectant in order to prevent microbiological growth in the membrane filtration units, the growth being due to high temperatures occurring during said membrane filtrations, so that growth of microbes will rapidly multiply, the respective growth likewise giving rise to a great number of other drawbacks.
The washing and cleaning effects may be improved in tubular membranes by including spherical bodies in the washing liquid, which bodies exert a mechanical cleaning action upon the membranes. In membrane units consisting of helically wound membrane modules, only washing liquid is used which may contain a desinfectant in a later stage.
The difficulty with this known method of washing and cleaning a plurality of membrane filtration units aligned in series, is that special measures have to be taken for separating the washing liquid for the various membrane filtration units aligned in series, so that special close-off valves have to be applied for introducing the washing liquid through various different consecutive membrane filtration units. Furthermore, the known method of washing and cleaning membrane filtration units demands much energy.